The present invention relates to a printing apparatus which is capable of printing on a booklet, such as bankbook, composed of a plurality of papers bound at one side. The printing apparatus is of the thermal transfer printing type.
A wire dot printing type of apparatuses has frequently been used for printing on a booklet, such as a bankbook, composed of a plurality of papers. For instance, in one wire dot print manner, the bankbook whose thickness is changed in accordance with a page to be printed is pressed against a reference guide by means of a platen, so that a printing surface position is always kept constant to be effected printing with means of the wire dot printing type. According to this printing method, it is advantageous to easily provide an apparatus that is capable of performing a clear print on a printing medium whose thickness is to be changed. It is, however, necessary to release the pressed condition of the bankbook whenever a print is started at a new line on a page. This needs an extra operation time. Thus, there is a disadvantage in enhancing the printing performance.
Also, in the above-described printing method, since the wire dot print means is used for printing, there is a problem that printing noises are large.
In order to solve this printing noise problem, it has been proposed to use a thermal transfer printing method in printing on a booklet. An example of this method is shown in Japanese Patent Unexamined Publication No. 34465/1981. In this printing manner, a thermal printing head is moved in a line direction for performing a print of a single line. However, when the print line of the bankbook is renewed after one printing operation, it is necessary to release the depression of the thermal print head. As in the wire dot print manner, it would be difficult to enhance the printing performance.
As described above, in the prior art, there is a problem such that it takes a long time to renew lines of the bankbook and it is difficult to enhance the printing performance.
A line dot type thermal printing method, in which a thermal ink film is depressed against a platen through a thermal printing head by means of a spring to thereby perform a printing, is known as a printing method which is capable of performing the printing without needs to release the depressed condition of the thermal printing head during the renewing operation of the lines on papers.
In a printer of this type, the printing medium and the thermal ink film are simultaneously and continuously fed by the rotation of the platen roller, thereby performing the feed of the printing medium. For this reason, it is unnecessary to release the depressed condition of the thermal head during the paper feed operation. It is, therefore, possible to perform a high speed printing operation.
Such a printing system involves the following disadvantages, when it is applied to a printer for printing a booklet composed of a plurality of papers such as a bankbook.
As is well known in the art, in order to obtain a clear print by a thermal printer, it is necessary to enhance a contactability among the printing paper, the thermal head and the thermal ink film. Since intermediate papers of a bankbook are relatively thin, when the bankbook is fed under the depressed condition with a large depression pressure while keeping a good contactability, a displacement or offset of the intermediate papers would be caused, resulting in inflation of the papers. This would cause problems such as a printing displacement or a jam of the bankbook or the thermal ink film.
In order to solve the above-described problems, it would be possible to perform the printing by reducing the depression pressure of the thermal head to a certain level. In this case, since the contactability between the bankbook, the thermal ink film and the thermal head would be degraded, the obtained print would be unclear. Otherwise, in order solve the problems, it would be possible to prolong an application time period of pulses to be applied to a heating resistor of the thermal head, thereby performing the printing with a high printing energy. However, in this case, the printing speed is of course slow down, so that it would be impossible to perform the printing at a desired printing speed.